It is known that calcium phosphates have a high affinity with biological materials (e.g. DNAs, proteins, and bones), cells, microorganisms, and the like. Among calcium phosphates, apatites have a bio-affinity. Especially, hydroxyapatites have a high affinity. Further, the hydroxyapatites are known as inorganic components constituting a bone of a living body, together with collagen. The hydroxyapatites have become a focus of attention since they can be used as functional material having biocompatibility (e.g. materials for artificial tooth and artificial bone) because of their living body components and their high affinity.
For example, it is considered that by combination of a structure containing a hydroxyapatite that is a calcium phosphate (hydroxyapatite structure) with living organisms, such as cells and microorganisms, it is possible to produce a biosensor, bioreactor, artificial organ, and the like which use a sensing capability, a material producing capability, and a physiological capability of such living organisms.
Examples of a method for manufacturing such a hydroxyapatite structure include a wet process using the reaction of an aqueous solution, a dry process using solid-phase reaction at a high temperature, a hydrothermal process in which single crystal is grown at a high temperature and at a high pressure, and biomimetic method in which a hydroxyapatite is grown under the conditions close to the conditions of a body's inner environment. Among these methods, especially the biomimetic method is superior in that it can form a hydroxyapatite structure having a large surface area, a high bio-affinity and a high bioactivity.
Non-patent Document 1 specifically discloses a method for obtaining a hydroxyapatite by biomimetic method. Patent Document 1 discloses a method of coating an entire target substance with calcium phosphates by biomimetic method.
As disclosed in these documents, seed crystal as a seed is needed for the growth of calcium phosphates. In these documents, CaO—SiO2 glass powder and a resin film are brought into contact in a simulated body fluid and the resulting solution is let stand for several days, whereby a seed crystal is precipitated on the surface of the film. The thus obtained seed crystal is used as a seed for the growth of calcium phosphates.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 59001/2005
(Tokukai 2005-59001; Published on Mar. 10, 2005)
[Non-patent Document]
Masami Tanahashi, et al., J. Am. Ceram. Soc., 77 (11) 2805-808 (1994)
As described previously, a method of precipitating a seed crystal as a seed on the surface of a solid, such as the previously described method using glass powder and a resin film has been carried out to obtain a seed for the growth of calcium phosphates. However, the method using such glass powder raises the problem that it needs a complicated step, including a step of separating the seed crystal from these solids.
An object of the present invention is to provide a method for stabilizing calcium phosphates fine particles, which method was not carried out in the past, and to provide a use of this method, for example, a method for manufacturing calcium phosphates fine particles.